Top 30 questions – asked in Microsoft SDE

Prepare for your next Microsoft Software Development Engineer (SDE) interview with these 30 essential questions and answers! From data structures and algorithms to Java-specific concepts, we’ve compiled the most frequently asked interview questions that test your problem-solving, coding skills, and understanding of computer science fundamentals. Whether you’re a seasoned developer or just starting, this guide will help you get ready for success. Don’t miss out on the key insights to ace your interview!

1. What is the difference between ArrayList and LinkedList?

• Answer: ArrayList is backed by a dynamic array, making access time O(1) but inserts/removals O(n). LinkedList is backed by a doubly linked list, which allows O(1) insertion and deletion but O(n) for access.

2. What is a HashMap and how does it work?

• Answer: A HashMap is a collection of key-value pairs, and it works by computing a hash value of the key to determine where to store the value. It provides O(1) average time complexity for lookups, inserts, and deletions.

3. What is the difference between final, finally, and finalize?

• Answer:
  • final: Used to define constants, prevent method overriding, or prevent class inheritance.
  • finally: A block of code that is always executed after a try-catch block.
  • finalize: A method that is called by the garbage collector before an object is destroyed.

4. What is the difference between == and .equals() in Java?

• Answer: == checks for reference equality (if two references point to the same object), while .equals() checks for logical equality (if the objects are meaningfully equal).

5. Explain the concept of polymorphism.

• Answer: Polymorphism allows one interface to be used for different data types. It can be achieved through method overriding (runtime polymorphism) or method overloading (compile-time polymorphism).

6. What is the time complexity of searching in a binary search tree (BST)?

• Answer: The time complexity for searching in a balanced BST is O(log n), but it can degrade to O(n) if the tree becomes unbalanced.

7. Explain the concept of thread synchronization.

• Answer: Thread synchronization ensures that two or more threads do not access shared resources concurrently, preventing data corruption. This can be done using synchronized blocks or methods.

8. What is a deadlock? How can it be prevented?

• Answer: A deadlock occurs when two or more threads are blocked forever, each waiting for the other to release a resource. Deadlocks can be prevented by ensuring that resources are always acquired in a consistent order or by using timeouts.

9. What is the difference between StringBuilder and StringBuffer?

• Answer: Both StringBuilder and StringBuffer are used to create mutable strings, but StringBuffer is thread-safe, while StringBuilder is not, offering better performance in single-threaded environments.

10. What is the Big-O time complexity of quicksort?

• Answer: On average, the time complexity of quicksort is O(n log n), but in the worst case, it can be O(n^2) if the pivot selection is poor.

11. What is the purpose of the transient keyword in Java?

• Answer: The transient keyword is used to mark fields of a class that should not be serialized.

12. What is the difference between a shallow copy and a deep copy?

• Answer: A shallow copy copies the values of an object, but references to other objects are shared. A deep copy copies all objects recursively, creating independent copies of all referenced objects.

13. What are the different types of sorting algorithms?

• Answer: Common sorting algorithms include Bubble Sort, Merge Sort, Quick Sort, Insertion Sort, and Selection Sort, each with different time and space complexities.

14. How does a database index work?

• Answer: A database index improves query performance by providing a quick lookup of data in a table. It works like a book’s index, allowing faster searching without scanning the entire table.

15. What is the purpose of the volatile keyword in Java?

• Answer: The volatile keyword is used to indicate that a variable may be changed by multiple threads, ensuring that the most recent value is always used by all threads.

16. What is a race condition?

• Answer: A race condition occurs when two or more threads access shared data simultaneously, and the final outcome depends on the non-deterministic ordering of thread execution.

17. What is a memory leak?

• Answer: A memory leak happens when memory that is no longer needed is not released, causing the program to consume more and more memory over time.

18. Explain the concept of a “factory pattern.”

• Answer: The Factory Pattern is a creational design pattern that provides an interface for creating objects, but the actual creation is left to subclasses or a factory class.

19. What is a stack and how does it work?

• Answer: A stack is a data structure that follows Last In, First Out (LIFO) order. Elements are pushed onto the stack, and popped off in reverse order.

20. What is the difference between while and do-while loops?

• Answer: In a while loop, the condition is checked before each iteration. In a do-while loop, the condition is checked after the first iteration, ensuring that the loop runs at least once.

21. What is the Singleton Design Pattern?

• Answer: The Singleton Pattern ensures that a class has only one instance and provides a global point of access to that instance.

22. What is a priority queue?

• Answer: A priority queue is a data structure where each element is associated with a priority, and elements are dequeued in order of their priority (highest or lowest).

23. What is a linked list and what are its types?

• Answer: A linked list is a linear data structure where each element (node) points to the next. Types include singly linked lists, doubly linked lists, and circular linked lists.

24. What is the difference between a HashMap and a TreeMap?

• Answer: A HashMap is an unordered collection of key-value pairs with O(1) time complexity for most operations. A TreeMap is a sorted map that uses a Red-Black tree and provides O(log n) time complexity for operations.

25. Explain the concept of recursion.

• Answer: Recursion is when a function calls itself to solve smaller instances of a problem. It generally involves a base case to stop the recursive calls.

26. What is the purpose of the super keyword in Java?

• Answer: The super keyword is used to refer to the superclass of the current object. It can be used to access superclass methods, constructors, and fields.

27. What is the time complexity of insertion sort?

• Answer: The time complexity of insertion sort is O(n^2) in the worst case and O(n) in the best case when the list is already sorted.

28. What is a binary heap?

• Answer: A binary heap is a complete binary tree used to implement priority queues. It satisfies the heap property: the value of each node is greater than or equal to (for max heap) or less than or equal to (for min heap) the values of its children.

29. What is the difference between a class and an interface in Java?

• Answer: A class defines the implementation of objects, while an interface defines a contract that classes can implement. A class can implement multiple interfaces but only inherit from one class.

30. What is a lambda expression?

• Answer: A lambda expression is a shorthand way to define anonymous functions in Java. It provides a clear and concise syntax for writing functional code.

These questions cover a wide range of topics and can help you prepare for a Microsoft SDE interview. Good luck!